Some Speculations about Applying Varnish
Several days of warm winter weather brought daily high temperatures just warm enough for applying varnish after using some incandescent shop lights beneath the boat to warm the hull. In part because of the brevity of this warm spell, I decided to apply each of my final finish coats "hot" -- i.e., before the smell of the drying paint had fully dissipated.
Most experts insist that you must sand between coats to give the varnish some "tooth" that it can latch onto. The premise seems to be that a smooth gloss finish gives the new coat of paint too little to grip. Sanding is used to create a three-dimensional surface to which the fresh varnish can attach itself. And this implies that the bond itself is a mechanical one instead of a chemical one.
Frankly, I'm skeptical by nature and I'm especially skeptical of this reasoning. If the roughness of the surface is essential, then it should be preferable to sand with rough sandpaper instead of smooth sandpaper -- 110 or 220 grit, instead of 320 or 400. Yet none of the experts makes such a distinction. None of them discourages sanding with 400 grit, yet such a fine sandpaper scarcely roughens a fully dry surface at all.
After much reflection, I have concluded that the bond between coats of paint is probably chemical rather than mechanical. I believe the reason for sanding dry paint before re-coating it is to remove some of the thin, hard, oxidized surface layer. Whenever I have wet-sanded between fully dry coats, I have noticed the strong smell of varnish in the rag with which I wiped the boat down -- and perhaps even some smell of varnish from the boat itself. Furthermore, anyone who has sanded off a blob of varnish knows that the surface of the blob can be very hard while the inside remains soft (and smelly) for weeks, months, or years. I think the same thing is at work in sanding between "fully dry" coats. Once the oxidized surface is removed, the solvents in the new paint can mix with the solvents now exposed in the older layer, and chemical bonding can take place.
Now consider a thin coat of high-gloss varnish. I can get six coats out of just a quart of varnish (and I must keep each coat thin to avoid drips). Most of the volume of that paint as it is applied is actually solvents that evaporate fairly rapidly. So, once dry, the layer of paint is very thin indeed. Thus, if I were to sand between coats, I would be quite likely to remove most (or all) of the varnish I just applied. But if the paint is not entirely dry between thin coats (i.e., it is still off-gassing the solvents), then the new paint will have a chance to form a chemical bond with the old, and sanding should be unnecessary. This is especially true if one "refreshes" the solvents by wiping down the hull with denatured alcohol just before applying the new varnish.
Only time will tell if I am correct in these speculations. But it is my boat, and the worst that can happen is that I have to sand it down and start over. I'll update this blog if my varnish starts to flake off in the next six months or so.
(Update 10/8/16) Having subjected the boat to an entire season of use, I am pleased to report that the varnish has held up extremely well. There are, of course, a few scratches and dings, but the boat may not even need a touch-up for next spring.
(Update 12/11/2019) I lightly sanded and re-varnished the interior last spring -- in part because I wanted to switch from a matte finish to high gloss. The exterior of the hull is still in very good condition after four seasons of use. No problems with the coats of varnish adhering to each other.
A Safe Method for Turning the Boat
Early in the building process, the Northeaster Dory is light enough for two reasonably strong men to lift and turn easily, but as the boat accumulates fiberglass, hardware, and paint, it becomes somewhat heavier. Ultimately I decided to use a rope harness to lift and turn the boat.
Here is a picture that shows the system in overview:
The red rope is 1/2" rescue line capable of lifting thousands of pounds. Obviously one does not need rope that strong, but it is what I had on hand. Any 3/8" line should work equally well. I threw an end over a beam in the garage and tied a bowline, with the working end danging down to support the boat.
A loop of 1/4" black line is created from a three or four foot chunk of line using double fishermen's bends. Here is a nice web page about tying that knot:
This loop of line is connected to the 3/8" working line with a Prussik.
The two loops of white line can be any strong webbing made into a loop with an overhand follow through bend (or water knot). Alternatively, one can use a double wrap of 1/4" line or a single wrap of 3/8" line. Again, that line is made into a loop using double fishermen's bends. As you can see from the close-ups, I used D-rings to connect the white lifting loop to the black Prussik loop.
Lowering the boat just reverses the process. Once person lifts the boat to remove the weight from the Prussik. The other person reaches up, gently loosens the Prussik, and slides the knot down to the desired position.
That's all there is to lifting and lowering the hull.
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After months of challenging and interesting work and one final flipping of the hull, I now have a beautiful and complete Chesapeake Light Craft Northeaster Dory. With an ever-so-slightly regretful sigh of relief, I now bring this construction journal to --
THE END
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| They call it a "tombstone transom"! . . . A fitting terminal image |
How cool is that, looks like a chinese junk floating Lake Norfork! I'll be watching for ya, we live due west of the 101 bridge on Teal Point and see all the cool boats. P.S. Have you ever seen the A-10's screaming along the lake?
ReplyDeleteDo watch for me. I only get as far as Teal Point when I go on a camping cruise, but I may do another one in the spring. I think somebody on Tracy Ferry Road is building a dory, so we may soon have two on the lake.
ReplyDelete